Locking unit

Abstract

A locking unit for the parking lock of an automatic transmission, for locking the movement of a piston which is movable by a drive and which can be acted on with hydraulic pressure.

What is claimed is: 
     
       1. A locking unit for a parking lock of an automatic transmission, for locking a movement of a piston which can be acted on with hydraulic pressure, comprising:
 the piston; 
 a housing; 
 a tube piece contained within the housing, wherein the piston is contained within the tube piece, wherein the tube piece has an aperture formed therein; 
 a pressure-conducting channel which is at least partially delimited radially to an outside, in relation to a longitudinal axis of the piston, by an inner wall of the housing, wherein the pressure-conducting channel is at least partially delimited to an inside by an outer side of the tube piece; 
 a pressure chamber formed between the piston and an inside of the tube piece, wherein the pressure chamber is fluidly connected to the pressure-conducting channel via the aperture that is formed in the tube piece, wherein the pressure-conducting channel guides a pressurized medium through the aperture and into the pressure chamber for actuation of the piston; and 
 at least one overpressure valve fluidically connected to the pressure-conducting channel and having a valve seat, wherein the valve seat is formed integrally with the housing 
 with the housing,
 wherein the at least one overpressure valve is arranged opposite a feed opening in the housing. 
 
 
     
     
       2. The locking unit as claimed in  claim 1 , wherein the housing is formed from plastic in a section that delimits the pressure-conducting channel. 
     
     
       3. The locking unit as claimed in  claim 1 , wherein the valve seat is formed integrally with the housing by overmolding of the valve seat. 
     
     
       4. The locking unit as claimed in  claim 1 , wherein the valve seat is formed integrally with the housing by monolithic injection-molding of the valve seat. 
     
     
       5. The locking unit as claimed in  claim 1 , wherein the valve seat is formed integrally with the housing by joining of the valve seat and the housing. 
     
     
       6. The locking unit as claimed in  claim 1 , wherein the at least one overpressure valve is arranged in a fluid path for the pressurized medium downstream of a filter element for the pressurized medium. 
     
     
       7. The locking unit as claimed in  claim 6 , wherein a closure part of the at least one overpressure valve is spring-preloaded into a closed setting of the at least one overpressure valve by at least one spring element. 
     
     
       8. The locking unit as claimed in  claim 7 , wherein the at least one overpressure valve has an opening travel delimitation for the closure part. 
     
     
       9. The locking unit as claimed in  claim 8 , wherein the opening travel delimitation has a delimiting element against which the closure part can abut to limit an opening travel. 
     
     
       10. The locking unit as claimed in  claim 9 , wherein the delimiting element has a central channel running in an opening travel direction. 
     
     
       11. The locking unit as claimed in  claim 7 , wherein the at least one overpressure valve has a closure part guide element which guides the closure part along its adjustment travel. 
     
     
       12. The locking unit as claimed in  claim 11 , the closure part guide element having fluid grooves running radially on the outside in an adjustment travel direction. 
     
     
       13. The locking unit as claimed in  claim 1 , wherein the at least one overpressure valve is formed in the housing so as to be directly fluidically connected to a feed prechamber or the pressure-conducting channel. 
     
     
       14. The locking unit as claimed in  claim 1 , wherein a wall thickness of the housing is configured for hydraulic internal pressures of up to 30 bar. 
     
     
       15. The locking unit as claimed in  claim 1 , wherein a wall thickness of the housing is configured for hydraulic internal pressures of up to 25 bar. 
     
     
       16. The locking unit as claimed in  claim 1 , wherein a wall thickness of the housing is configured for hydraulic internal pressures of up to 21 bar. 
     
     
       17. The locking unit as claimed in  claim 1 , further comprising:
 a middle piece connected to the tube piece of the housing, wherein the middle piece forms a bearing surface for the piston. 
 
     
     
       18. The locking unit as claimed in  claim 17 , wherein the piston comprises a piston tube piece and a piston thrust piece, wherein the middle piece forms the bearing surface for the piston thrust piece. 
     
     
       19. The locking unit of  claim 18 , wherein at least part of the piston thrust piece is contained in the tube piece of the housing.